For an inflatable packer to form an effective seal against the surrounding walls of a well bore, the mid-portion thereof should lead the expansion during inflation and thus touch the walls first. On the other hand, if the end portions engage and seal first, well fluids can be trapped in an annular volume between such end portions and the packer will not properly seal off. Where the packer has long lengths of external armor such as overlapped slats or cable, there can be preferential expansion which traps fluid pockets as mentioned. Occasionally an elastomer cover over the center of the armor is employed, which can cause fluids to be trapped in annular pockets between each end on the packer and such central cover. Another problem encountered in inflatable packer setting is that the inner elastomer bladder which is arranged underneath the armor can inflate initially in such a way that a bubble is formed so that the bladder does not conform to the armor assembly. This can result in the formation of Z-folds, particularly where the energy to continue radial expansion of the bladder is greater than the energy to extend it axially over an uninflated portion of the bladder. A Z-fold causes non-uniform expansion of the bladder and ultimately can cause rupture.
Some efforts have been made to control the shape of an inflatable packer as it is inflated. For example U.S. Pat. Nos. 4,832,120 and 4,951,747 disclose systems where shear screws between the packer piston and the mandrel provide a degree of axial restraint. However these structures influence packer shape only during the very initial part of the first inflation, and further are inoperable for any additional packer settings. Thus a shear pin mechanism is not an effective way to control the shape of the packer element during inflation.
The present invention utilizes the concept that axial loads that are applied to the packer armor assembly, whether slats or cables, tend to increase the radial stiffness of such assembly. When sufficiently high axial loads are applied, the effect of the external central cover is minimized and the packer tends to have expansion at its mid-portion first during inflation. Moreover, the stiffness of armor assembly, whether it be overlapped slats or longitudinal cables, dominates bladder inflation behavious so that the inner bladder conforms to the armor during the entire inflation process to eliminate Z-folding of the bladder walls.
An object of the present invention is to provide a new and improved inflatable packer system including means to control the shape of the packer element during most of the inflation process in a manner that assures an effective packoff.
Another object of the present invention is to provide a new and improved inflatable packer system including means for applying axial loading to the packer element during inflation in a manner that controls the shape thereof during outward expansion into sealing engagement with a surrounding wall.
Another object of the present invention is to provide a new and improved inflatable packer system that includes a piston whose movement is restrained in a manner such that axial loads are applied which control inflation shape and prevent Z-folding of the inner bladder.
Another object of the present invention is to provide a new and improved inflatable packer system and method where a resilient means is employed to generate restraining forces which control the shape and deployment of the packer element during expansion.
Yet another object of the present invention is to provide a new and improved inflatable packer system where friction forces are generated to control the shape and deployment of the packer element during expansion thereof.
Another object of the present invention is to provide a new and improved inflatable packer system where continuously generated shear forces are employed to control the shape and deployment of the packer element during expansion thereof.
Another object of the present invention is to provide a new and improved inflatable packer system where swaging loads are employed to control the inflation shape of the packer.
Yet another object of the present invention is to provide a new and improved inflatable packer system where crushing of a sleeve member provides restraining forces that control the inflation shape of the packer element.
Still another object of the present invention is to provide a new and improved inflatable packer assembly that is constructed and arranged to obviate the various problems with prior devices noted above.